Machine tools typically include a driven body that is rotationally driven or driven by traveling by a motor, such as a main spindle, a headstock, and a tool post. Normally, the driven body is stored in a cover provided with a door, and a workpiece grasped by the main spindle is machined therein. The door is provided to be freely opened and closed and thus, opening the door allows maintenance on the driven body inside the cover.
In such a machine tool, if the motor drives the driven body during maintenance, then maintenance is interrupted and, further, safety may not be able to be ensured. Thus, there are provided machine tools that each include a drive regulation device provided with a detection unit for detecting an open state and a closed state of the door and a motor regulation unit for regulating a rotation of the motor so as to stop the rotation of the motor when the door is in the open state.
As an example of the motor regulation unit, a speed regulation unit has been known that, when an unexpected rotation such as an erroneous operation occurs on the motor that has been stopped, if the rotation speed of the motor exceeds a predetermined allowable rotation speed, an error occurs at a control apparatus side to stop the motor (e.g., refer to Patent Literature 1). The allowable rotation speed is set to be an extremely low speed so that an operator can easily handle the case even if the unexpected rotation occurs on the motor. When the door is opened, the motor is stopped by the operation of the speed regulation unit and, additionally, even when the rotation of the motor erroneously occurs, an unexpected high-speed rotation of the motor can be prevented since only the extremely low speed is allowed for the allowable rotation speed.
Further, as the motor regulation unit, an excitation stop unit has been also known that cuts a power source to be supplied to the motor when the door is in the open state so as to make the motor non-excited to stop the motor, and also regulates the unexpected rotation of the motor (e.g., refer to Patent Literature 2)